Honestly I can't stand one piece...
Too long
Too much DBZ stand around and talk at each other
It really didn't need to be almost 500 episodes long and still going.
He is still hasn't even gotten the pirate treasure or w/e he wanted. (I don't think anyway)
All of the plot elements could easily have been condensed into less than 100 episodes, without much loss.
To me tbh, the perfect anime length is 50 episodes.
Any longer and the pacing moves along at the pace of a snail in absolute zero, or it gets so ridiculous, and over the top when compared to its origins it isn't even the same show anymore.
At some point your character doesn't really need to undergo any more changes, and you should just bring the show to a conclusion.
Powering characters down isn't really that satisfying, I mean if he had the ability to single-handedly blow up a fkin planet, he shouldn't later have difficulty defeating some shrubbery in his lawn.
Any-shorter, and you always want it to go on longer.
D. Gray Man so far is the only anime I am glad went on more than 50 episodes as of yet.
PS: That elk thing creeps me the hell out.